Electric blasting cap



April 20 1926.

1,581,799 H. 1.. GRANT ELECTRIC BLASTING CAP Original Filed July 22, l92

amuenfoz Patented Apr. 20, 1926. I 1

UNITED STATES PATENT oF'FIcE.

HARRY L. GRANT, OF TAMAQUA, PENNSYLVANIA, ASSIG NOIR TO ATLAS POWDER COM- IPANY, OF WILMINGTON, DELAWARE, A CQRPORATION OF DELAWARE.

' ELECTRIC BLASTING car:

Original application filed July 22, 1925, Serial No. 45,327. Divided and this application flied December 7, 1925. Serial No. 73,637.

To all whom it may concern: Be it known that HARRY L. GRANT, citizen of the United States, residing at Tamaqua, in the county of Schuylkill and State of Pennsylvania, has invented certain new and useful Improvements in Electric Blasting Caps, of which the following is a specification.

This invention has for its object to pro vide an electric blasting cap which cannot be prematurely exploded by accidentally, or otherwise, coming in contact with stray electric currents, of any nature, either while being transported or actually used on the job. This application is divisional to my pending application No.45327, filed July 22, 1925.

Many cases have been recorded where loss of life and destruction of property have been caused by premature explosions of dynamite or other commercial explosives. There was a cause for each of these accidents. Cases are on record where a shot has been prepared for firing and which has prematurely exploded, apparently without cause. It is thus seen that the cause for premature explosions is not always visible'to an observer. With the ever increasing use of electrical power and electric labor saving appliances in and about coal mines and quarries and construction projects, there is always the possibility of encountering stray electric currents. ing through moist earth, between the source of supply and bad joints or bonds of trolley rails or on water or steam pi es. The average electric blasting cap '0 present American manufacture can be fired by impressing across the ends of its lead wires an E. M. F. of from one to two volts. Potentials of this order cannot be detected without the aid of electrical measuring instruments. Many tests have been made wherein considerably higher potentials have been recorded and yetcould not. be detected by Among the objects of my invention is to provide an electrically insulated fuse head or igniting device for the electric blasting cap, in order that grounding of the lead These currents may be found flow wires or short circuiting of same by touch ing the s1de wall of the metal shell, will be prevented. This insulation will make it lmpossible to complete a circuit through mechanically support or prevent separation of the lead wires; this now being accomplished by a metal fuse head covered by U. S. Patent 1,407,167 issued to Charles C. Jessen.

A further object is to provide a fuse head for an electric blasting cap, insulated from the charge in the base ofthe shell and from the side wall of the metal shell and which can be used in connection with a safety shunt or some means of short circuiting the exposed ends of the lead wires. lVhen this, has been done the electric blasting cap cannot be exploded .by the electric current so long as the safety shunt is in place. My new electric blasting cap differs in this respect from other types of electric blasting caps, except the match head type. and differs from the former match-head type in that the efliciency of the insulation is not dependent upon special 1 invention will be set forth in the detailed description which now follows:

In the accompanying drawing:

Fig. 1 is a side elevation of an assembled electric detonator constructed in accordance with the invention,

Fig. 2 is a vertical sectional view through the cap portion thereof, upon an enlarged scale, and

Fig. 3 is a detail view, upon an enlarged scale, of a shunt hereinafter described.

Like numerals designate corresponding parts in all of the figures of the drawing.

Referring to the drawing, 5 designates the shell of the detonator. These shells are usually formed of copperor gilding metal, though the invention is not limited to use in conjunction with tlcular klnd.

Electric detonators now commonly in use material of any parutilize igniting elements comprlsing aball thein length, as indicated at 12 and 13, and

the outer ends of these lead wires are usually left bare, as indicated at 14 and 15, to adapt them for ready connection to the usual firing cable leading from the blasting ma chine, (not shown).

The present invention resides in the em ployment of a tube 16, of fibre, or other suitable insulating material, in which the ignition assembly is held in centered relation 2y means of a body of sealing material 17.

be lower end of the tube is closed and in-' dented, as indicated at 18, and the matchhead projects from the indented end but does not project beyond the line of the lower edge of the tube.

The charge to be fired by the match-head is indicated at 19, and may comprise a body of mercury fulminate, though any suitable material may be used' 'in this relation- The upper or outer end of the charge 19; is in-' dented and the lower edge of the tube rests directly upon the charge, the space between the charge and the match-head being what is usually known as fuse head clearance. After the charge 19 has been placed in the shell 5, the ignition assembly, consisting of the electrical elements, the tube 16 and the body'o'f'sealing material 17, are inserted in the shell and secured in place by a second body of sealing material of a di-electric and water-proof nature, that is indicated at 20. The shell 5 is preferably provided with an annular groove 21, into which the body of sealing material 20' projects, in such way as to resist longitudinal movement of the body of'sealing material with respect to the shell 5. It is to be noted that the insulation 12 and 13, extends downwardly from the wires 7 and 8 to a point below the line of the top of the tube 16. In process of assembly,

. the fuse head passes through a waterproofing operation and is treated with a waterproof and dielectric substance, such as nitro-cellulose varnish, which thoroughly insulates the explosive or flame producing composition, on its lower end, from contact with any form of electrical conductor.

By virtue of the construction described, the electrical circuit element and the fuse head are wholly, electrically, separated from the charge. in the base'of the shell and from,

the metal shell 5. The separation of the fuse head from the charge 19 is made positive by the projection 18 of the tube 16, in-

conjunction with contact of the lower end of the tube 16 with the indented charge 19, 1t being understood that this charge 1s not a loosecharge but is of such a nature as to maintain its form and to be held in place by the engagement of tube 16, therewith.

In Fig. 3, I have illustrated a' metallic shunt 22, which is disposed directly at the end of the insulation upon the lead wires and which consists of a body of soft metal,

pressed into engagement with the lead wires after they have been disposed in crossed relation, andserves to hold the lead wires in contact with each other. Thus, a short circult is created between the lead wires,-so that if the outer ends of said lead wires come in contact with sources of stray electric current, the current cannot pass beyond the shunt constituted by the body 23., Thus, the exposed ends of the lead wires :are protected by the shunt at the outer end of the structure and since the electrical elements and the match-head at the inner end of the structure are protected by the tube 16 and the coatin of dielectric material upon the match-hea it follows that this detonator cannot, under any circumstances, be accidentally exploded by stray electric currents. The shunt 23, of Fig. 3 requires no further description in this app 'cation since it has been made the subject matter of a separate application for patent and is not claimed herein.

It is to be understood that the invention is not limited to the precise construction set forth but that it includes within its purview whatever changes fairly come within either the terms or the spirit of the appended c aims.

Having described my invention, what I claim is:

1. An electric detonator comprising a shell, a charge of explosive material there-I in, an electrical fuse head assembly, a tube of insulating material having an open upper end and a closed lower end, in which the fuse head assembly is disposed, a body of sealing material fillin said tube and binding the fuse head assem ly therein, the lower end of the fuse head projecting throu h the.

bottom of the tube and a water-proo sealing material within the shell above said .tube, the exposed lower end of the fuse head being coated with a highly dielectric material to electrically insulate it from. the charge.

2. An electric detonator comprising a shell, a body of explosive material therein .of such consistency as to maintain-its form,

said body having an indented up r end, a cylindrical tube in said shell an closely conforming to the internal dlameter there 'shell and to thereby in the fuse head assembly is coated with a highly dielectric material.

4. A structure as recited in claim 2, wherein the shell is provided with an annular internal groove for the reception of the outer sealing material, to prevent longitudinal movement of the same with respect to the hold theseveral parts in assembled relation within said shell.

In testimony whereof he alfixes his signature.

HARRY L. GRANT. 

